Quantitative determination and explanation for geometric characteristics of joints in deep rock mass are fundamental to investigate mechanical properties and permeability

and in particular they are the main factors to determine the site of nuclear waste reserve and evaluation. Based on the modified data of joint number from three boreholes of BS17

BS18

BS19 in Beishan

Gansu province

a negative exponential-like distribution mathematical model is established. Furthermore the model is applied to evaluate the integrity of deep rock mass in rock quality designation (RQD) system. The reliability of the model is verified by comparing with rock integrity designation (RID) results. It should be pointed out that there is a piecewise function of a linear relationship between the joint number and spacing

and the fractal dimension increases with the spacing expanding. According to the power-law between the joint number and spacing

there is a multi-fractal relationship between them

as well as the joint number and depth. The multi-fractal spectrum is suggested to analyze the statistical data of joint geometric shape and distribution. The results provide a reference for 3D simulation of joints in deep rock mass based on geometrical characteristics of borecore joints.